JPH0670393B2 - Engine fuel controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel control device for an engine in a vehicle or the like that burns fuel at an optimum air-fuel ratio.

[Conventional technology]

FIG. 5 is a schematic configuration diagram showing a conventional fuel control device for an engine, in which 1 is an engine, 2 is an intake manifold, and 3 is attached to the intake manifold 2 so as to face the vicinity of an intake port of the engine 1. Fuel injection valve, 4
Is a surge tank for intake pressure provided between the intake manifold 3 and the intake pipe 5, 6 is a throttle valve provided in the intake pipe 5, and 7 is an air flow sensor provided near the upstream end of the intake pipe 5. , So as to be located inside a ring-shaped air duct, for example. The air flow sensor 7 is an air flow rate measuring device based on the principle of heat dissipation, which obtains data of air weight including temperature and density of intake air as an output. 8 is a rotation sensor 9 for detecting the rotation speed of the engine 1.
Is a control device that calculates and determines the optimum fuel injection amount based on each of the output of the air flow sensor 7 and the output of the air flow sensor 7.

The control device 8 has a computer configuration shown in FIG. That is, 81 is an analog / digital converter (hereinafter referred to as an A / D converter) that converts the analog output of the air flow sensor 7 into a digital signal that is convenient for arithmetic processing.
Reference numeral 83 is an interface circuit for taking in the digital output of the rotation sensor 9, reference numeral 83 is a microprocessor (hereinafter referred to as CPU) for calculating an optimum supply amount based on the outputs of the A / D converter 81 and the interface circuit 82, 84 Is a memory (hereinafter referred to as RAM) for temporarily storing various data (including the above outputs) used during calculation, 85 is a memory for storing data such as calculation procedure (hereinafter referred to as ROM), and 86 is output from the microprocessor 83. This is an amplifier that widens the fuel supply amount signal to be used.

Next, the operation will be described.

The output obtained from the air flow sensor 7 includes the normal ripples as shown in (a) of FIG. 7 when the engine 1 is operating in a state other than the vicinity where the throttle valve 6 is fully open (WOT). Since a true intake air weight can be obtained by calculating the area surrounded by this waveform, the drive pulse width of the fuel injection valve 3 is calculated based on the value obtained by dividing the intake air amount by the microprocessor 83 by the engine speed. Is controlled to obtain a desired air-fuel ratio.

However, in an engine with four or less cylinders, the output waveform of the air flow sensor 7 due to the blowback from the engine 1 in a specific rotation speed region (generally 1000 to 3000 ppm) near WOT is shown in FIG. ), The shaded portion is added to the true intake air amount.

This is because the hot-wire type air flow sensor 7 detects and outputs the intake air amount regardless of the flow direction of the air.

As shown in FIG. 8, the detection error due to this blowback differs depending on the rotational speed, and normally the intake pipe negative pressure occurs from around −50 mmHg and reaches a maximum of 50% in the WOT region.

When the fuel supply amount is calculated and injected using a value including such a large error, the air-fuel ratio becomes significantly rich, and the fuel becomes unstable and cannot be put to practical use. As described above, for the region a in which an error is caused by blowback, the maximum air amount determined corresponding to the engine is set as the upper limit value (the value shown by the broken line), and the upper limit value is stored in the ROM 85. As shown in (b) of the figure, the detection value of the air flow sensor 7 that exceeds this value is clipped at the upper limit value to prevent the air-fuel ratio from becoming excessively rich.

[Problems to be solved by the invention]

Since the conventional engine fuel control device is configured as described above, the upper limit value of the intake air amount must be set in accordance with the intake air amount characteristic of the target engine in the lowland, and therefore it is inevitable. It is the upper limit of the mass flow rate in the lowlands.

However, for example, when a high load operation is performed in a high altitude where the atmospheric pressure is low, the average value of the output level of the air flow sensor 7 reaches a predetermined upper limit value as shown in (c) of Fig. 7 due to the decrease of the air density. Therefore, the average value of the output level including blowback is used as it is for fuel calculation.
The air-fuel ratio shifts to the latch side. Therefore, the air-fuel ratio fluctuates with respect to the atmospheric pressure as shown in FIG. That is, if the upper limit value of the intake air amount is determined by the atmospheric pressure, there is a problem that the error of the air-fuel ratio becomes large between the highland where the atmospheric pressure is low and the highland where the atmospheric pressure is high.

The present invention has been made to solve the above problems, and eliminates the error of the air-fuel ratio due to the change in atmospheric pressure,
An object of the present invention is to obtain an engine fuel control device that can ensure a stable combustion state under all engine operating conditions.

[Means for solving problems]

The engine fuel supply device according to the present invention is configured such that an atmospheric pressure sensor that detects the atmospheric pressure near the engine and a maximum intake air amount that changes substantially in proportion to the engine speed when the throttle valve is fully opened are provided in advance. An upper limit value setting unit that sets an upper limit value of the intake air amount according to the engine speed, a correction unit that corrects the upper limit value by the atmospheric pressure detected by the atmospheric pressure sensor, and an output of the air flow sensor is corrected. And a limiter that uses the corrected upper limit value as the output of the air flow sensor when the upper limit value is exceeded.

[Action]

In the engine fuel control device according to the present invention,
The error in the air-fuel ratio that differs due to the difference in atmospheric pressure is corrected by using the correction value data that cancels out according to the difference in atmospheric pressure, and the arithmetic output of the microprocessor that takes this correction value data into account The data controls the amount of combustion injection by the combustion injection valve. Therefore, regardless of this change in atmospheric pressure, the measurement error of the intake air amount due to the blowback of the engine is eliminated, a stable and constant air-fuel ratio is always obtained, the combustion of the air-fuel mixture is stabilized, and the engine output is also stabilized. Act as you do.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. First
In the figure, reference numeral 10 is an atmospheric pressure sensor for detecting the atmospheric pressure around the engine 1 mounted on the vehicle, and is composed of, for example, a semiconductor strain gauge in which a change in the atmospheric pressure is attached to a diaphragm means or the like. The atmospheric pressure sensor 10 inputs the detected atmospheric pressure data to the control device 8 described above. In addition,
Other than that, the same components as those shown in FIG. 5 are designated by the same reference numerals, and the duplicate description thereof will be omitted.

Next, the operation will be described.

When the engine 1 is operated, intake air is sent into the intake manifold 2 via the air cleaner and the intake pipe 5, and then the combustion injection valve 3 provided in the intake manifold 2 for each cylinder is kept at a constant timing. Inject fuel,
The air-fuel mixture with the preset air-fuel ratio is sent to the combustion chamber of the cylinder. At this time, the atmospheric pressure is detected by the atmospheric pressure sensor 10, and its output is input to the A / D converter 81 in the control device 8, where it is converted into a digital signal and further input to the microprocessor 83.

Next, the arithmetic processing executed by the microprocessor 83 using the atmospheric pressure data detected as described above will be described according to the flow chart of FIG.

First, the air flow sensor 7 reads the intake air amount Qa (step 100), and then reads the atmospheric pressure Bp around the engine 1 from the atmospheric pressure sensor 10 (step 101). Next, at low altitude, the clip value Qu (CLIP) of the intake air amount determined according to the engine speed is multiplied by the atmospheric pressure correction coefficient C (BP) of FIG. , Clip correction value Qc is obtained (step 102). Subsequently, it is determined whether or not the measured intake air amount Qa is larger than the clip correction value Qc (step 103), and if QaQc, set Q = Qa (step 104), and if Qa> Qc, set Q = Qc (step). Ten
Five). Next, the rotation speed Ne is read from the rotation sensor 9 (step 106), Q / Ne is calculated and used as the data of the pulse width τ of the combustion injection valve 3 (step 107).

By such an arithmetic processing operation, the upper limit value of the intake air amount is always a value corrected by the atmospheric pressure, so that the air-fuel ratio error due to the difference in the atmospheric pressure in the traveling area in the operating region near the full opening of the throttle valve 6 is eliminated. Therefore, stable combustion of the air-fuel mixture and stable operation of the engine can be realized.

〔The invention's effect〕

As described above, according to the present invention, the atmospheric pressure sensor for detecting the atmospheric pressure around the engine is provided, and the upper limit value of the intake air amount is set in the operating region of the engine in which the air flow sensor does not show the true value of the intake air amount. Since it is configured to be corrected by the output of the atmospheric pressure sensor, regardless of whether the place is high or low, it is possible to eliminate the measurement error of the intake air amount due to engine blowback and obtain a stable air-fuel ratio. There is an effect that a mixture capable of forming the above-mentioned air-fuel mixture and ensuring the combustion state can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an engine fuel control apparatus according to a first embodiment of the present invention, FIG. 2 is a block connection diagram showing a main portion of the control apparatus, and FIG. 3 is an atmospheric pressure correction coefficient used in the present invention. FIG. 4 is a characteristic diagram, FIG. 4 is a flow chart showing arithmetic processing by a microprocessor, FIG. 5 is a schematic configuration diagram of a conventional fuel supply control device, FIG. 6 is a block connection diagram of the control device in FIG. 5, and FIG. FIG. 8 is an output characteristic diagram of the air flow sensor, FIG. 8 is a detection error characteristic diagram of the air flow sensor, FIG. 9 is a characteristic diagram of the output of the air flow sensor with respect to the engine speed, and FIG. 10 is an air-fuel ratio error characteristic diagram. 1 is an engine, 3 is a fuel injection valve, 7 is an air flow sensor, 8 is a control device, and 10 is an atmospheric pressure sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukinobu Nishimura 840 Chiyoda-cho, Himeji City, Hyogo Prefecture Mitsubishi Electric Corporation Himeji Plant (56) References JP-A-59-190431 (JP, A) JP-A-58- 131329 (JP, A) JP-A-55-43292 (JP, A)

Claims (3)

[Claims] 1. A fuel control device for an engine for determining a basic fuel supply amount based on an intake air amount of an engine detected by an air flow sensor for detecting a mass flow rate and an engine speed detected by a rotation sensor. The atmospheric pressure sensor that detects the atmospheric pressure of the engine and the upper limit of the intake air amount that corresponds to the engine speed in advance so as to correspond to the maximum intake air amount that changes substantially in proportion to the engine speed when the throttle valve is fully opened. Is set, correction means for correcting the upper limit value by the atmospheric pressure detected by the atmospheric pressure sensor, and the correction is made when the output of the air flow sensor exceeds the corrected upper limit value. And a limiter that uses the upper limit value as the output of the air flow sensor. 2. The fuel control device for an engine according to claim 1, wherein the air flow sensor is a hot wire type air flow sensor. 3. The fuel control device for an engine according to claim 1, wherein the atmospheric pressure sensor is a semiconductor strain gauge.